I’ve just started an antibiotics course which is 4 times a day for 10 days and that got me wondering if they would be just as effective if I took them all and why not.
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Drugs only stay in your body for a limited time, and it takes time for them to find their targets. The drugs and the bacteria pretty much have to randomly run into each other in your bloodstream or wherever. So if you took it all at once some of the bacteria would survive no matter how much you took. Taking the meds over a period of time keeps a supply in your body long enough to kill all the bacteria, or to kill enough that your immune system can handle the rest. Good question tho. It makes sense to wonder how this works.
Moreover, some antibiotics can only interfer with bacteria in certain stages of their life, e.g. by inhibiting reproduction/cell division.
You essentially put them under siege, until they are massacred by the immune system or die of other reasons.
If you dont finish the course, the bacteria can grow resistant to the active ingredients
Drugs have half-lives in the body, which means that half of the drug, no matter the dose, is gone in a certain time. If you take it all at once, “half” is a big amount which is excreted or broken down quickly, wasting lots of the drug. What you want is a relatively steady concentration of the drug over a long time.
Also, drugs have side effects, and an unnecessarily high dose will give you more side effects. Many drugs can even cause fatal poisonings when overdosed.
The second chart on this page shows how the concentration of a drug in the body rises, and then reaches a steady oscillation between two values, as you take consecutive doses: https://www.ama-assn.org/medical-students/usmle-step-1-2/kaplan-usmle-step-1-prep-what-s-half-life-investigational-drug
very simply, it’s like drinking water. If you drink enough water for a week in a day, your body can’t deal with it all, you’ll need to pee real bad and you’ll feel terrible. The water will be wasted and by the end of the week you’ll be really thirsty!
You need to match the input with what your body can process and how quickly the antibiotics work.
In addition to what others have said, azithromycin (Zithromax) can sometimes be taken in a single dose. This is especially useful when patients are unlikely to complete a full course on their own.
It’s a similar reason to why you eat or drink several times a day. Your body is constantly processing and flushing out waste. The purpose of antibiotics is to make your body a hostile environment to an infection. That only works until the infection is completely eliminated, and if the antibiotic is flushed from your system too soon the infection will potentially grow back.
Antibiotics tend to not remain in your system for long, and you wouldn’t want them to linger in your system. Newer ones are probably more targeted, but, in concept, they literally are poison, and can potentially harm beneficial microbes as well, which is why diarrhea and digestive issues are often side-effects of antibiotics. Your digestive system relies on a lot of microbes that technically aren’t part of your body to help break down things you eat. So you don’t want to take a single larger dose, because it would potentially have toxic side effects for your body.
A number of folks have mentioned that antibiotics (abx) are excreted from your body rather quickly. What’s happening is that most of the abx excreted (let’s call it 75% but it varies wildly) but only a portion is absorbed (20%) and only a small portion (5%) makes it to where the infection is. You need multiple doses to have enough abx where it does some good; you can’t do it all at once (anymore than you can drink 5 gallons of water all at once).
My great aunt used to always take them all at once, swore by it she was one of them old people that wouldn’t listen to common sense. Loved nothing more than washing her phone in the bath every other month also then wondering why it broke… she died a few years back at the age of 98, had a heart attack whist cleaning her lights up a ladder they think. Don’t make them like that anymore!
A couple of things are happening here, first is that when you put something into your body, it either breaks it down into parts to build cells, or it gets rid of it (at least it tries to).
The other is that to completely kill off the bacteria, they need to be exposed to the drugs for a prolonged period of time.
If you took all the antibiotics at once, one of two things would happen: One possibility is that the drugs spend a very brief time in your system before they get flushed out, so the bacteria would only be exposed to a very high dose briefly, which might kill more of them at first but still leave a bunch to continue growing the infection. The other possibility is that such a high dose of antibiotics would overwhelm the systems in your body that take care of “getting rid of stuff” like the kidneys and liver and damage them. Neither option is good for you.
Antibiotics kill a bunch of bacteria, and then wear off. When they wear off, the most resistant germs survive and can multiply and evolve.
If we repeat the dose, the antibiotics don’t wear off. It’s a lot harder for even the most resistant germs to survive for long enough to multiply, which reduces evolution.
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